1. Field of the Invention
The present invention generally relates to an ignition timing control system for an internal combustion engine. More particularly, the present invention relates to an ignition timing control system which performs fast catalytic warm-up by adjusting the ignition timing for an internal combustion engine.
2. Description of the Related Art
Fast catalytic warm-up technique has been well known as a technique to reduce noxious substance contained in burnt gas exhausted from an internal combustion engine in the engine start operation. When the internal combustion engine is in the cold state, the catalytic converter included in the exhaust system is also in the cold state and can not sufficiently work to clean the exhaust gas until it has been warmed up to the specified temperature. The fast catalytic warm-up technique is therefore a technique to retard the ignition timing in order to facilitate the warm-up of the catalytic converter.
Specifically, this ignition timing retard technique applicable to the internal combustion engine in the cold state facilitates the warm-up of the catalytic converter by having the internal combustion engine burn in the stage near the exhaust stroke and introducing high temperature exhaust gas into the catalytic converter.
This technique, however, is not advantageous in that when the ignition timing is retarded immediately after the start of the internal combustion engine when the internal combustion engine is in the cold state, the rotational speed of the internal combustion engine that should increase immediately after the start thereof does not increase accordingly.
In order to solve this problem, a new technique to control the ignition timing according to both the cooling water temperature and the time passed after the start of the internal combustion engine was proposed. It is a technique to warm-up the catalyst when the cooling water temperature is low by retarding the ignition timing only after the specified time has passed instead of retarding the ignition timing immediately after the start of the internal combustion engine. (Japanese Unexamined Patent Publication No. 62-103464.)
Nevertheless, this newly proposed technique still has problem as described in the following, and therefore has been unable to be an appropriate substitution for the first-mentioned technique.
The problem in question is: when the internal combustion engine restarts at a low temperature, while the cooling water temperature has not yet been cooled down so much, part around the intake air port of the internal combustion engine has been cooled down by the cold atmosphere. If the ignition timing retard is sharply controlled in such state by using the proposed technique, fuel would adhere to the cold part around the intake air port, then a sufficient amount of fuel could not be supplied into the cylinders, and consequently engine stalling would be caused.